1. Field of the Invention
This invention relates to electrical counter circuits. In particular the invention relates to counter circuits for counting dial pulses generated by a dial pulse relay apparatus associated with a key telephone station set.
2. Description of the Prior Art
In prior art key telephone apparatus, malfunctions in counter circuits used in signalling apparatus have occurred when an erroneous pulse or pulses, similar to a dial pulse, enters the counting circuit. Erroneous pulses can be generated when the handset is lifted from the telephone station for the purpose of placing an extension call over an intercom line. The erroneous pulses occur because of mechanical hookswitch bounding or fumbling when the handset is lifted.
One approach in the prior art to solve this problem has been to attempt to make mechanical changes in the hookswitch construction in order to eliminate hookswitch bounce. This approach has not been very successful because of mechanical constraints in the design of the telephone set.
A general object of this invention is to provide a new and improved counter circuit for use in a key telephone system which ignores or absorbs erroneous pulses occurring as a result of hookswitch bounce.
A further object of this invention is to provide a new and improved counter circuit for use in signalling apparatus associated with a key telephone system.
Another object of this invention is to provide a counter circuit for use in a key telephone signalling system which disregards erroneous pulses generated by hookswitch bouncing or fumbling.
It is another object of this invention to provide a counter circuit which returns to its reset state if the count of the number of pulses in the first pulse train arriving at the counter circuit is less than a predetermined number n of pulses where 1 &lt; n &lt; 7.